In manufacturing integrated circuit (IC) devices, a batch type vertical diffusion and chemical vapor diffusion (CVD) system (hereinafter, “a batch-type CVD system”) is widely used to diffuse impurities onto wafers or to form on the wafers CVD films such as insulating films, metal films or the like.
In substrate processing apparatuses including the batch-type CVD system, a plurality of wafers are transferred while being contained in a carrier. Two kinds of carriers have been conventionally used. One is a box-shaped cassette having a pair of openings on two opposite sides thereof and the other is a box-shaped FOUP (front opening unified pod; hereinafter, “pod”) having an opening on one side thereof with a pod door removably mounted thereon. When the pod is used as a carrier for the wafers, the wafers can be kept protected from contaminations of ambient atmosphere while being transferred since the pod containing the wafers is airtightly closed. Accordingly, the requirement of cleanliness for a clean room in which the substrate processing apparatus is installed can be relaxed, thereby reducing the cost for maintenance of the clean room. For such reasons, the pod is gaining popularity as a wafer carrier in the batch-type CVD system recently.
In general, a batch-type CVD system having a pod as a wafer carrier includes a process tube for performing a desired process to wafers, a boat for loading/unloading a plurality, e.g. 150 sheets, of wafers into/from the process tube, a wafer loading port for supporting one or more pods while the wafers are transferred between the pods and the boat, a pod stage for placing thereon pods unloaded from and to be introduced into the CVD system, pod shelves for temporarily storing pods and a pod transfer device for conducting pod transfer between the pod stage and the pod shelves and between the pod shelves and the wafer loading port.
In such a batch-type CVD system described above, the pods are carried to the pod stage and then transferred by the pod transfer device to the pod shelves to be temporarily kept thereon. Then, a plurality of pods kept on the pod shelves are transferred to the wafer loading port through repetitive operations of the pod transfer device. Thereafter, the wafers contained in the pods are charged into the boat by the wafer transfer device and then the boat is loaded into the process tube in which the wafers are processed. The processed wafers are unloaded from the process tube and discharged from the boat to be carried into the empty pods waiting on the wafer loading port through the repetitive operations of the wafer transfer device. The pods containing the processed wafers therein are repeatedly transferred to the pod stage by the pod transfer device after being temporarily kept on the pod shelves.
Recently, in manufacturing large scale integration (LSI) devices or the like, a quick turned around time (QTAT) type production, in which the required time from input of wafers to finish is as shortened as possible, is gaining importance. The QTAT manufacturing method has increased a demand for a small-batch type CVD system suitable for processing 25 sheets or less of wafers during one batch process, i.e., for a small batch process. Such a small-batch type CVD system requires only two or three pods for one batch process.
However, the above described conventional batch-type CVD system is suitable for a large batch dealing with a large number, e.g., 150 sheets, of substrates during one batch process. Accordingly, the footprint required for the pod shelves or the number of layers of each pod shelf should be increased or the shelves should be built to be rotatable so as to accommodate many pods thereon. Thus, the use of such a conventional batch-type CVD system for a small batch process would end up with the unnecessarily large and complicated system. Further, initial costs or running costs of the system would also be unnecessarily increased. Still further, the conventional batch-type CVD system cannot fully meet requirements of the QTAT type production.